percpu_ref: add PERCPU_REF_INIT_* flags
With the recent addition of percpu_ref_reinit(), percpu_ref now can be
used as a persistent switch which can be turned on and off repeatedly
where turning off maps to killing the ref and waiting for it to drain;
however, there currently isn't a way to initialize a percpu_ref in its
off (killed and drained) state, which can be inconvenient for certain
persistent switch use cases.
Similarly, percpu_ref_switch_to_atomic/percpu() allow dynamic
selection of operation mode; however, currently a newly initialized
percpu_ref is always in percpu mode making it impossible to avoid the
latency overhead of switching to atomic mode.
This patch adds @flags to percpu_ref_init() and implements the
following flags.
* PERCPU_REF_INIT_ATOMIC : start ref in atomic mode
* PERCPU_REF_INIT_DEAD : start ref killed and drained
These flags should be able to serve the above two use cases.
v2: target_core_tpg.c conversion was missing. Fixed.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 44a78ae..d85fe01 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1796,7 +1796,7 @@
goto err_hctxs;
if (percpu_ref_init(&q->mq_usage_counter, blk_mq_usage_counter_release,
- GFP_KERNEL))
+ 0, GFP_KERNEL))
goto err_map;
setup_timer(&q->timeout, blk_mq_rq_timer, (unsigned long) q);
diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index 4ab6da3..be783f7 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -819,7 +819,7 @@
{
int ret;
- ret = percpu_ref_init(&lun->lun_ref, core_tpg_lun_ref_release,
+ ret = percpu_ref_init(&lun->lun_ref, core_tpg_lun_ref_release, 0,
GFP_KERNEL);
if (ret < 0)
return ret;
diff --git a/fs/aio.c b/fs/aio.c
index 8d217ed..84a7510 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -661,10 +661,10 @@
INIT_LIST_HEAD(&ctx->active_reqs);
- if (percpu_ref_init(&ctx->users, free_ioctx_users, GFP_KERNEL))
+ if (percpu_ref_init(&ctx->users, free_ioctx_users, 0, GFP_KERNEL))
goto err;
- if (percpu_ref_init(&ctx->reqs, free_ioctx_reqs, GFP_KERNEL))
+ if (percpu_ref_init(&ctx->reqs, free_ioctx_reqs, 0, GFP_KERNEL))
goto err;
ctx->cpu = alloc_percpu(struct kioctx_cpu);
diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index cd7e20f..b0293f2 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -63,6 +63,21 @@
__PERCPU_REF_FLAG_BITS = 2,
};
+/* @flags for percpu_ref_init() */
+enum {
+ /*
+ * Start w/ ref == 1 in atomic mode. Can be switched to percpu
+ * operation using percpu_ref_switch_to_percpu().
+ */
+ PERCPU_REF_INIT_ATOMIC = 1 << 0,
+
+ /*
+ * Start dead w/ ref == 0 in atomic mode. Must be revived with
+ * percpu_ref_reinit() before used. Implies INIT_ATOMIC.
+ */
+ PERCPU_REF_INIT_DEAD = 1 << 1,
+};
+
struct percpu_ref {
atomic_long_t count;
/*
@@ -76,7 +91,8 @@
};
int __must_check percpu_ref_init(struct percpu_ref *ref,
- percpu_ref_func_t *release, gfp_t gfp);
+ percpu_ref_func_t *release, unsigned int flags,
+ gfp_t gfp);
void percpu_ref_exit(struct percpu_ref *ref);
void percpu_ref_switch_to_atomic(struct percpu_ref *ref,
percpu_ref_func_t *confirm_switch);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a99d504..753df01 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1634,7 +1634,8 @@
goto out;
root_cgrp->id = ret;
- ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, GFP_KERNEL);
+ ret = percpu_ref_init(&root_cgrp->self.refcnt, css_release, 0,
+ GFP_KERNEL);
if (ret)
goto out;
@@ -4510,7 +4511,7 @@
init_and_link_css(css, ss, cgrp);
- err = percpu_ref_init(&css->refcnt, css_release, GFP_KERNEL);
+ err = percpu_ref_init(&css->refcnt, css_release, 0, GFP_KERNEL);
if (err)
goto err_free_css;
@@ -4583,7 +4584,7 @@
goto out_unlock;
}
- ret = percpu_ref_init(&cgrp->self.refcnt, css_release, GFP_KERNEL);
+ ret = percpu_ref_init(&cgrp->self.refcnt, css_release, 0, GFP_KERNEL);
if (ret)
goto out_free_cgrp;
diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c
index 5a6d43b..ed280fb 100644
--- a/lib/percpu-refcount.c
+++ b/lib/percpu-refcount.c
@@ -45,27 +45,40 @@
* percpu_ref_init - initialize a percpu refcount
* @ref: percpu_ref to initialize
* @release: function which will be called when refcount hits 0
+ * @flags: PERCPU_REF_INIT_* flags
* @gfp: allocation mask to use
*
- * Initializes the refcount in single atomic counter mode with a refcount of 1;
- * analagous to atomic_long_set(ref, 1).
+ * Initializes @ref. If @flags is zero, @ref starts in percpu mode with a
+ * refcount of 1; analagous to atomic_long_set(ref, 1). See the
+ * definitions of PERCPU_REF_INIT_* flags for flag behaviors.
*
* Note that @release must not sleep - it may potentially be called from RCU
* callback context by percpu_ref_kill().
*/
int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release,
- gfp_t gfp)
+ unsigned int flags, gfp_t gfp)
{
size_t align = max_t(size_t, 1 << __PERCPU_REF_FLAG_BITS,
__alignof__(unsigned long));
-
- atomic_long_set(&ref->count, 1 + PERCPU_COUNT_BIAS);
+ unsigned long start_count = 0;
ref->percpu_count_ptr = (unsigned long)
__alloc_percpu_gfp(sizeof(unsigned long), align, gfp);
if (!ref->percpu_count_ptr)
return -ENOMEM;
+ if (flags & (PERCPU_REF_INIT_ATOMIC | PERCPU_REF_INIT_DEAD))
+ ref->percpu_count_ptr |= __PERCPU_REF_ATOMIC;
+ else
+ start_count += PERCPU_COUNT_BIAS;
+
+ if (flags & PERCPU_REF_INIT_DEAD)
+ ref->percpu_count_ptr |= __PERCPU_REF_DEAD;
+ else
+ start_count++;
+
+ atomic_long_set(&ref->count, start_count);
+
ref->release = release;
return 0;
}